Traditionally, computer systems are designed to be able to continuously run a fairly worst-case thermal load corresponding to a worst-case workload. Designs according to such a continuous worst-case load have never been much of a problem, because traditionally the individual components have had modest operating power consumptions and the computer systems have had considerable cooling capacity so that the systems could sustain the load fairly naturally.
As the operating power consumptions of the individual components of computer system creep upwards, the thermal budgets of the computer systems have become tighter. The systems have become more difficult to cool. It is now becoming a challenge to design a computer system to run continuously at the worst-case thermal load while pursuing other high performance goals, such as high computing power, compactness, quietness, better battery performance, etc.
The thermal management system of a computer system typically includes a closed-loop temperature control, which includes a temperature sensor and a controller to regulate either the cooling system or the power generation to achieve a desired temperature, typically below a maximum allowable temperature. The closed-loop temperature controller constantly measures the temperature of the computer system through the temperature sensor, and controls the system cooling parameters such as a fan speed to keep the system temperature under the temperature limit. Further, the controller can adjust the system temperature by changing the heat generation within the computer system, either by adjusting the power or the frequency. There are various methodologies to control the temperature using a closed-loop temperature control system, with the popular method being a PID controller, which varies the amount of the system's heating generation or cooling capacity depending on the temperature difference.
One of the critical issues in thermal management system is the location of the temperature sensor since the system temperature distribution is likely not uniform, and therefore the temperature sensor is typically best located in the hottest location to assure that the whole system is under the temperature limit.
Current computer systems do not provide convenient or ideal locations for temperature sensors. A further temperature control problem associated with current computer systems is the variation of hottest temperature locations, occurring due to the optional components that can be dynamically inserted or removed. For examples, a floppy drive may or may not be installed, an extra video card may be installed, a CD drive may be exchanged with an extra battery, a PCI card may or may not be installed, etc. Each system configuration has its own ideal location for a temperature sensor, and therefore the multiple system configurations make an optimum temperature sensor placement difficult and often impractical. A thermal control system which does not have an accurate way to measure a “system” temperature is forced to assume the worst case thermal scenario.
For a system where the optimum temperature sensor location changes with user's configurations, a thermal control system is blind to certain critical component temperatures and certain system configurations, and is forced to assume the worst, resulting in a reduced performance or an overcooled system with unpleasant acoustic output (e.g. the noise of a fan) due to excessive cooling operations.